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588df31a | 1 | .\" -*- nroff -*- |
2 | .\" | |
3 | .\" Author: Tatu Ylonen <ylo@cs.hut.fi> | |
4 | .\" Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland | |
5 | .\" All rights reserved | |
6 | .\" | |
7 | .\" As far as I am concerned, the code I have written for this software | |
8 | .\" can be used freely for any purpose. Any derived versions of this | |
9 | .\" software must be clearly marked as such, and if the derived work is | |
10 | .\" incompatible with the protocol description in the RFC file, it must be | |
11 | .\" called by a name other than "ssh" or "Secure Shell". | |
12 | .\" | |
13 | .\" Copyright (c) 1999,2000 Markus Friedl. All rights reserved. | |
14 | .\" Copyright (c) 1999 Aaron Campbell. All rights reserved. | |
15 | .\" Copyright (c) 1999 Theo de Raadt. All rights reserved. | |
16 | .\" | |
17 | .\" Redistribution and use in source and binary forms, with or without | |
18 | .\" modification, are permitted provided that the following conditions | |
19 | .\" are met: | |
20 | .\" 1. Redistributions of source code must retain the above copyright | |
21 | .\" notice, this list of conditions and the following disclaimer. | |
22 | .\" 2. Redistributions in binary form must reproduce the above copyright | |
23 | .\" notice, this list of conditions and the following disclaimer in the | |
24 | .\" documentation and/or other materials provided with the distribution. | |
25 | .\" | |
26 | .\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR | |
27 | .\" IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES | |
28 | .\" OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. | |
29 | .\" IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, | |
30 | .\" INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT | |
31 | .\" NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, | |
32 | .\" DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY | |
33 | .\" THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT | |
34 | .\" (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF | |
35 | .\" THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. | |
36 | .\" | |
f444d0f8 | 37 | .\" $OpenBSD: sshd_config.5,v 1.76 2007/06/07 19:37:34 pvalchev Exp $ |
e473dcd1 | 38 | .Dd $Mdocdate$ |
588df31a | 39 | .Dt SSHD_CONFIG 5 |
40 | .Os | |
41 | .Sh NAME | |
42 | .Nm sshd_config | |
43 | .Nd OpenSSH SSH daemon configuration file | |
44 | .Sh SYNOPSIS | |
5d9a4204 | 45 | .Nm /etc/ssh/sshd_config |
588df31a | 46 | .Sh DESCRIPTION |
32cfd177 | 47 | .Xr sshd 8 |
588df31a | 48 | reads configuration data from |
49 | .Pa /etc/ssh/sshd_config | |
50 | (or the file specified with | |
51 | .Fl f | |
52 | on the command line). | |
53 | The file contains keyword-argument pairs, one per line. | |
54 | Lines starting with | |
55 | .Ql # | |
56 | and empty lines are interpreted as comments. | |
533b9133 | 57 | Arguments may optionally be enclosed in double quotes |
58 | .Pq \&" | |
59 | in order to represent arguments containing spaces. | |
588df31a | 60 | .Pp |
61 | The possible | |
62 | keywords and their meanings are as follows (note that | |
63 | keywords are case-insensitive and arguments are case-sensitive): | |
64 | .Bl -tag -width Ds | |
61a2c1da | 65 | .It Cm AcceptEnv |
66 | Specifies what environment variables sent by the client will be copied into | |
67 | the session's | |
68 | .Xr environ 7 . | |
69 | See | |
70 | .Cm SendEnv | |
71 | in | |
72 | .Xr ssh_config 5 | |
73 | for how to configure the client. | |
b8b9f2e6 | 74 | Note that environment passing is only supported for protocol 2. |
61a2c1da | 75 | Variables are specified by name, which may contain the wildcard characters |
f09ffbdb | 76 | .Ql * |
61a2c1da | 77 | and |
78 | .Ql \&? . | |
b8b9f2e6 | 79 | Multiple environment variables may be separated by whitespace or spread |
61a2c1da | 80 | across multiple |
81 | .Cm AcceptEnv | |
82 | directives. | |
b8b9f2e6 | 83 | Be warned that some environment variables could be used to bypass restricted |
61a2c1da | 84 | user environments. |
85 | For this reason, care should be taken in the use of this directive. | |
86 | The default is not to accept any environment variables. | |
31b41ceb | 87 | .It Cm AddressFamily |
88 | Specifies which address family should be used by | |
32cfd177 | 89 | .Xr sshd 8 . |
31b41ceb | 90 | Valid arguments are |
91 | .Dq any , | |
92 | .Dq inet | |
b74c3b8c | 93 | (use IPv4 only), or |
31b41ceb | 94 | .Dq inet6 |
95 | (use IPv6 only). | |
96 | The default is | |
97 | .Dq any . | |
588df31a | 98 | .It Cm AllowGroups |
99 | This keyword can be followed by a list of group name patterns, separated | |
100 | by spaces. | |
101 | If specified, login is allowed only for users whose primary | |
102 | group or supplementary group list matches one of the patterns. | |
588df31a | 103 | Only group names are valid; a numerical group ID is not recognized. |
104 | By default, login is allowed for all groups. | |
84c1b530 | 105 | The allow/deny directives are processed in the following order: |
106 | .Cm DenyUsers , | |
107 | .Cm AllowUsers , | |
108 | .Cm DenyGroups , | |
109 | and finally | |
110 | .Cm AllowGroups . | |
ac1ec4d8 | 111 | .Pp |
112 | See | |
113 | .Sx PATTERNS | |
114 | in | |
115 | .Xr ssh_config 5 | |
116 | for more information on patterns. | |
588df31a | 117 | .It Cm AllowTcpForwarding |
118 | Specifies whether TCP forwarding is permitted. | |
119 | The default is | |
120 | .Dq yes . | |
121 | Note that disabling TCP forwarding does not improve security unless | |
122 | users are also denied shell access, as they can always install their | |
123 | own forwarders. | |
588df31a | 124 | .It Cm AllowUsers |
125 | This keyword can be followed by a list of user name patterns, separated | |
126 | by spaces. | |
1be697b6 | 127 | If specified, login is allowed only for user names that |
588df31a | 128 | match one of the patterns. |
588df31a | 129 | Only user names are valid; a numerical user ID is not recognized. |
130 | By default, login is allowed for all users. | |
131 | If the pattern takes the form USER@HOST then USER and HOST | |
132 | are separately checked, restricting logins to particular | |
133 | users from particular hosts. | |
84c1b530 | 134 | The allow/deny directives are processed in the following order: |
135 | .Cm DenyUsers , | |
136 | .Cm AllowUsers , | |
137 | .Cm DenyGroups , | |
138 | and finally | |
139 | .Cm AllowGroups . | |
ac1ec4d8 | 140 | .Pp |
141 | See | |
142 | .Sx PATTERNS | |
143 | in | |
144 | .Xr ssh_config 5 | |
145 | for more information on patterns. | |
588df31a | 146 | .It Cm AuthorizedKeysFile |
147 | Specifies the file that contains the public keys that can be used | |
148 | for user authentication. | |
149 | .Cm AuthorizedKeysFile | |
150 | may contain tokens of the form %T which are substituted during connection | |
b74c3b8c | 151 | setup. |
3cbc677d | 152 | The following tokens are defined: %% is replaced by a literal '%', |
b74c3b8c | 153 | %h is replaced by the home directory of the user being authenticated, and |
588df31a | 154 | %u is replaced by the username of that user. |
155 | After expansion, | |
156 | .Cm AuthorizedKeysFile | |
157 | is taken to be an absolute path or one relative to the user's home | |
158 | directory. | |
159 | The default is | |
160 | .Dq .ssh/authorized_keys . | |
161 | .It Cm Banner | |
162 | In some jurisdictions, sending a warning message before authentication | |
163 | may be relevant for getting legal protection. | |
164 | The contents of the specified file are sent to the remote user before | |
165 | authentication is allowed. | |
166 | This option is only available for protocol version 2. | |
167 | By default, no banner is displayed. | |
588df31a | 168 | .It Cm ChallengeResponseAuthentication |
340a4caf | 169 | Specifies whether challenge-response authentication is allowed. |
588df31a | 170 | All authentication styles from |
171 | .Xr login.conf 5 | |
172 | are supported. | |
173 | The default is | |
174 | .Dq yes . | |
175 | .It Cm Ciphers | |
176 | Specifies the ciphers allowed for protocol version 2. | |
177 | Multiple ciphers must be comma-separated. | |
3b9baa7b | 178 | The supported ciphers are |
179 | .Dq 3des-cbc , | |
180 | .Dq aes128-cbc , | |
181 | .Dq aes192-cbc , | |
182 | .Dq aes256-cbc , | |
183 | .Dq aes128-ctr , | |
184 | .Dq aes192-ctr , | |
185 | .Dq aes256-ctr , | |
74a66cc8 | 186 | .Dq arcfour128 , |
187 | .Dq arcfour256 , | |
3b9baa7b | 188 | .Dq arcfour , |
189 | .Dq blowfish-cbc , | |
190 | and | |
191 | .Dq cast128-cbc . | |
b74c3b8c | 192 | The default is: |
193 | .Bd -literal -offset 3n | |
194 | aes128-cbc,3des-cbc,blowfish-cbc,cast128-cbc,arcfour128, | |
195 | arcfour256,arcfour,aes192-cbc,aes256-cbc,aes128-ctr, | |
196 | aes192-ctr,aes256-ctr | |
588df31a | 197 | .Ed |
588df31a | 198 | .It Cm ClientAliveCountMax |
79e46360 | 199 | Sets the number of client alive messages (see below) which may be |
588df31a | 200 | sent without |
b74c3b8c | 201 | .Xr sshd 8 |
3cbc677d | 202 | receiving any messages back from the client. |
203 | If this threshold is reached while client alive messages are being sent, | |
b74c3b8c | 204 | sshd will disconnect the client, terminating the session. |
3cbc677d | 205 | It is important to note that the use of client alive messages is very |
206 | different from | |
fd573618 | 207 | .Cm TCPKeepAlive |
3cbc677d | 208 | (below). |
209 | The client alive messages are sent through the encrypted channel | |
210 | and therefore will not be spoofable. | |
211 | The TCP keepalive option enabled by | |
fd573618 | 212 | .Cm TCPKeepAlive |
3cbc677d | 213 | is spoofable. |
214 | The client alive mechanism is valuable when the client or | |
588df31a | 215 | server depend on knowing when a connection has become inactive. |
216 | .Pp | |
3cbc677d | 217 | The default value is 3. |
218 | If | |
588df31a | 219 | .Cm ClientAliveInterval |
79e46360 | 220 | (see below) is set to 15, and |
588df31a | 221 | .Cm ClientAliveCountMax |
b74c3b8c | 222 | is left at the default, unresponsive SSH clients |
588df31a | 223 | will be disconnected after approximately 45 seconds. |
2d762582 | 224 | This option applies to protocol version 2 only. |
2264526c | 225 | .It Cm ClientAliveInterval |
226 | Sets a timeout interval in seconds after which if no data has been received | |
227 | from the client, | |
b74c3b8c | 228 | .Xr sshd 8 |
2264526c | 229 | will send a message through the encrypted |
230 | channel to request a response from the client. | |
231 | The default | |
232 | is 0, indicating that these messages will not be sent to the client. | |
233 | This option applies to protocol version 2 only. | |
588df31a | 234 | .It Cm Compression |
07200973 | 235 | Specifies whether compression is allowed, or delayed until |
236 | the user has authenticated successfully. | |
588df31a | 237 | The argument must be |
07200973 | 238 | .Dq yes , |
239 | .Dq delayed , | |
588df31a | 240 | or |
241 | .Dq no . | |
242 | The default is | |
07200973 | 243 | .Dq delayed . |
588df31a | 244 | .It Cm DenyGroups |
245 | This keyword can be followed by a list of group name patterns, separated | |
246 | by spaces. | |
247 | Login is disallowed for users whose primary group or supplementary | |
248 | group list matches one of the patterns. | |
588df31a | 249 | Only group names are valid; a numerical group ID is not recognized. |
250 | By default, login is allowed for all groups. | |
84c1b530 | 251 | The allow/deny directives are processed in the following order: |
252 | .Cm DenyUsers , | |
253 | .Cm AllowUsers , | |
254 | .Cm DenyGroups , | |
255 | and finally | |
256 | .Cm AllowGroups . | |
ac1ec4d8 | 257 | .Pp |
258 | See | |
259 | .Sx PATTERNS | |
260 | in | |
261 | .Xr ssh_config 5 | |
262 | for more information on patterns. | |
588df31a | 263 | .It Cm DenyUsers |
264 | This keyword can be followed by a list of user name patterns, separated | |
265 | by spaces. | |
266 | Login is disallowed for user names that match one of the patterns. | |
588df31a | 267 | Only user names are valid; a numerical user ID is not recognized. |
268 | By default, login is allowed for all users. | |
269 | If the pattern takes the form USER@HOST then USER and HOST | |
270 | are separately checked, restricting logins to particular | |
271 | users from particular hosts. | |
84c1b530 | 272 | The allow/deny directives are processed in the following order: |
273 | .Cm DenyUsers , | |
274 | .Cm AllowUsers , | |
275 | .Cm DenyGroups , | |
276 | and finally | |
277 | .Cm AllowGroups . | |
ac1ec4d8 | 278 | .Pp |
279 | See | |
280 | .Sx PATTERNS | |
281 | in | |
282 | .Xr ssh_config 5 | |
283 | for more information on patterns. | |
e7259e8d | 284 | .It Cm ForceCommand |
285 | Forces the execution of the command specified by | |
286 | .Cm ForceCommand , | |
287 | ignoring any command supplied by the client. | |
288 | The command is invoked by using the user's login shell with the -c option. | |
289 | This applies to shell, command, or subsystem execution. | |
290 | It is most useful inside a | |
291 | .Cm Match | |
292 | block. | |
293 | The command originally supplied by the client is available in the | |
294 | .Ev SSH_ORIGINAL_COMMAND | |
295 | environment variable. | |
588df31a | 296 | .It Cm GatewayPorts |
297 | Specifies whether remote hosts are allowed to connect to ports | |
298 | forwarded for the client. | |
299 | By default, | |
b74c3b8c | 300 | .Xr sshd 8 |
a4e5acef | 301 | binds remote port forwardings to the loopback address. |
302 | This prevents other remote hosts from connecting to forwarded ports. | |
588df31a | 303 | .Cm GatewayPorts |
b74c3b8c | 304 | can be used to specify that sshd |
3867aa0a | 305 | should allow remote port forwardings to bind to non-loopback addresses, thus |
306 | allowing other hosts to connect. | |
307 | The argument may be | |
308 | .Dq no | |
309 | to force remote port forwardings to be available to the local host only, | |
588df31a | 310 | .Dq yes |
3867aa0a | 311 | to force remote port forwardings to bind to the wildcard address, or |
312 | .Dq clientspecified | |
313 | to allow the client to select the address to which the forwarding is bound. | |
588df31a | 314 | The default is |
315 | .Dq no . | |
7364bd04 | 316 | .It Cm GSSAPIAuthentication |
105b07db | 317 | Specifies whether user authentication based on GSSAPI is allowed. |
aff51935 | 318 | The default is |
7364bd04 | 319 | .Dq no . |
320 | Note that this option applies to protocol version 2 only. | |
321 | .It Cm GSSAPICleanupCredentials | |
322 | Specifies whether to automatically destroy the user's credentials cache | |
323 | on logout. | |
324 | The default is | |
325 | .Dq yes . | |
326 | Note that this option applies to protocol version 2 only. | |
588df31a | 327 | .It Cm HostbasedAuthentication |
328 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
329 | with successful public key client host authentication is allowed | |
340a4caf | 330 | (host-based authentication). |
588df31a | 331 | This option is similar to |
332 | .Cm RhostsRSAAuthentication | |
333 | and applies to protocol version 2 only. | |
334 | The default is | |
335 | .Dq no . | |
e9f2e744 | 336 | .It Cm HostbasedUsesNameFromPacketOnly |
337 | Specifies whether or not the server will attempt to perform a reverse | |
338 | name lookup when matching the name in the | |
339 | .Pa ~/.shosts , | |
340 | .Pa ~/.rhosts , | |
341 | and | |
342 | .Pa /etc/hosts.equiv | |
343 | files during | |
344 | .Cm HostbasedAuthentication . | |
345 | A setting of | |
346 | .Dq yes | |
347 | means that | |
348 | .Xr sshd 8 | |
349 | uses the name supplied by the client rather than | |
350 | attempting to resolve the name from the TCP connection itself. | |
351 | The default is | |
352 | .Dq no . | |
588df31a | 353 | .It Cm HostKey |
354 | Specifies a file containing a private host key | |
355 | used by SSH. | |
356 | The default is | |
357 | .Pa /etc/ssh/ssh_host_key | |
358 | for protocol version 1, and | |
359 | .Pa /etc/ssh/ssh_host_rsa_key | |
360 | and | |
361 | .Pa /etc/ssh/ssh_host_dsa_key | |
362 | for protocol version 2. | |
363 | Note that | |
b74c3b8c | 364 | .Xr sshd 8 |
588df31a | 365 | will refuse to use a file if it is group/world-accessible. |
366 | It is possible to have multiple host key files. | |
367 | .Dq rsa1 | |
368 | keys are used for version 1 and | |
369 | .Dq dsa | |
370 | or | |
371 | .Dq rsa | |
372 | are used for version 2 of the SSH protocol. | |
373 | .It Cm IgnoreRhosts | |
374 | Specifies that | |
375 | .Pa .rhosts | |
376 | and | |
377 | .Pa .shosts | |
378 | files will not be used in | |
588df31a | 379 | .Cm RhostsRSAAuthentication |
380 | or | |
381 | .Cm HostbasedAuthentication . | |
382 | .Pp | |
383 | .Pa /etc/hosts.equiv | |
384 | and | |
385 | .Pa /etc/shosts.equiv | |
386 | are still used. | |
387 | The default is | |
388 | .Dq yes . | |
389 | .It Cm IgnoreUserKnownHosts | |
390 | Specifies whether | |
b74c3b8c | 391 | .Xr sshd 8 |
588df31a | 392 | should ignore the user's |
140e3e97 | 393 | .Pa ~/.ssh/known_hosts |
588df31a | 394 | during |
395 | .Cm RhostsRSAAuthentication | |
396 | or | |
397 | .Cm HostbasedAuthentication . | |
398 | The default is | |
399 | .Dq no . | |
588df31a | 400 | .It Cm KerberosAuthentication |
8f73f7bb | 401 | Specifies whether the password provided by the user for |
588df31a | 402 | .Cm PasswordAuthentication |
8f73f7bb | 403 | will be validated through the Kerberos KDC. |
588df31a | 404 | To use this option, the server needs a |
405 | Kerberos servtab which allows the verification of the KDC's identity. | |
b74c3b8c | 406 | The default is |
588df31a | 407 | .Dq no . |
24f37810 | 408 | .It Cm KerberosGetAFSToken |
0d3d1077 | 409 | If AFS is active and the user has a Kerberos 5 TGT, attempt to acquire |
24f37810 | 410 | an AFS token before accessing the user's home directory. |
b74c3b8c | 411 | The default is |
24f37810 | 412 | .Dq no . |
588df31a | 413 | .It Cm KerberosOrLocalPasswd |
b74c3b8c | 414 | If password authentication through Kerberos fails then |
588df31a | 415 | the password will be validated via any additional local mechanism |
416 | such as | |
417 | .Pa /etc/passwd . | |
b74c3b8c | 418 | The default is |
588df31a | 419 | .Dq yes . |
588df31a | 420 | .It Cm KerberosTicketCleanup |
421 | Specifies whether to automatically destroy the user's ticket cache | |
422 | file on logout. | |
b74c3b8c | 423 | The default is |
588df31a | 424 | .Dq yes . |
425 | .It Cm KeyRegenerationInterval | |
426 | In protocol version 1, the ephemeral server key is automatically regenerated | |
427 | after this many seconds (if it has been used). | |
428 | The purpose of regeneration is to prevent | |
429 | decrypting captured sessions by later breaking into the machine and | |
430 | stealing the keys. | |
431 | The key is never stored anywhere. | |
432 | If the value is 0, the key is never regenerated. | |
433 | The default is 3600 (seconds). | |
434 | .It Cm ListenAddress | |
435 | Specifies the local addresses | |
b74c3b8c | 436 | .Xr sshd 8 |
588df31a | 437 | should listen on. |
438 | The following forms may be used: | |
439 | .Pp | |
440 | .Bl -item -offset indent -compact | |
441 | .It | |
442 | .Cm ListenAddress | |
443 | .Sm off | |
444 | .Ar host No | Ar IPv4_addr No | Ar IPv6_addr | |
445 | .Sm on | |
446 | .It | |
447 | .Cm ListenAddress | |
448 | .Sm off | |
449 | .Ar host No | Ar IPv4_addr No : Ar port | |
450 | .Sm on | |
451 | .It | |
452 | .Cm ListenAddress | |
453 | .Sm off | |
454 | .Oo | |
455 | .Ar host No | Ar IPv6_addr Oc : Ar port | |
456 | .Sm on | |
457 | .El | |
458 | .Pp | |
459 | If | |
460 | .Ar port | |
461 | is not specified, | |
b74c3b8c | 462 | sshd will listen on the address and all prior |
588df31a | 463 | .Cm Port |
3cbc677d | 464 | options specified. |
465 | The default is to listen on all local addresses. | |
a4e5acef | 466 | Multiple |
588df31a | 467 | .Cm ListenAddress |
3cbc677d | 468 | options are permitted. |
469 | Additionally, any | |
588df31a | 470 | .Cm Port |
b74c3b8c | 471 | options must precede this option for non-port qualified addresses. |
588df31a | 472 | .It Cm LoginGraceTime |
473 | The server disconnects after this time if the user has not | |
474 | successfully logged in. | |
475 | If the value is 0, there is no time limit. | |
3445ca02 | 476 | The default is 120 seconds. |
588df31a | 477 | .It Cm LogLevel |
478 | Gives the verbosity level that is used when logging messages from | |
32cfd177 | 479 | .Xr sshd 8 . |
588df31a | 480 | The possible values are: |
b74c3b8c | 481 | QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. |
a4e5acef | 482 | The default is INFO. |
483 | DEBUG and DEBUG1 are equivalent. | |
484 | DEBUG2 and DEBUG3 each specify higher levels of debugging output. | |
485 | Logging with a DEBUG level violates the privacy of users and is not recommended. | |
588df31a | 486 | .It Cm MACs |
487 | Specifies the available MAC (message authentication code) algorithms. | |
488 | The MAC algorithm is used in protocol version 2 | |
489 | for data integrity protection. | |
490 | Multiple algorithms must be comma-separated. | |
b74c3b8c | 491 | The default is: |
f444d0f8 | 492 | .Dq hmac-md5,hmac-sha1,umac-64@openssh.com,hmac-ripemd160,hmac-sha1-96,hmac-md5-96 . |
d231781a | 493 | .It Cm Match |
14e980ef | 494 | Introduces a conditional block. |
4895f836 | 495 | If all of the criteria on the |
d231781a | 496 | .Cm Match |
4895f836 | 497 | line are satisfied, the keywords on the following lines override those |
498 | set in the global section of the config file, until either another | |
d231781a | 499 | .Cm Match |
4895f836 | 500 | line or the end of the file. |
14e980ef | 501 | The arguments to |
d231781a | 502 | .Cm Match |
4895f836 | 503 | are one or more criteria-pattern pairs. |
d231781a | 504 | The available criteria are |
505 | .Cm User , | |
fa47fe3c | 506 | .Cm Group , |
d231781a | 507 | .Cm Host , |
508 | and | |
509 | .Cm Address . | |
510 | Only a subset of keywords may be used on the lines following a | |
511 | .Cm Match | |
512 | keyword. | |
513 | Available keywords are | |
2fefbadf | 514 | .Cm AllowTcpForwarding , |
03bcbf84 | 515 | .Cm Banner , |
e7259e8d | 516 | .Cm ForceCommand , |
2fefbadf | 517 | .Cm GatewayPorts , |
03bcbf84 | 518 | .Cm GSSApiAuthentication , |
121c4a34 | 519 | .Cm KbdInteractiveAuthentication , |
a863b75f | 520 | .Cm KerberosAuthentication , |
03bcbf84 | 521 | .Cm PasswordAuthentication , |
691712e0 | 522 | .Cm PermitOpen , |
03bcbf84 | 523 | .Cm RhostsRSAAuthentication , |
524 | .Cm RSAAuthentication , | |
691712e0 | 525 | .Cm X11DisplayOffset , |
526 | .Cm X11Forwarding , | |
d231781a | 527 | and |
691712e0 | 528 | .Cm X11UseLocalHost . |
af4bd935 | 529 | .It Cm MaxAuthTries |
530 | Specifies the maximum number of authentication attempts permitted per | |
8fca654b | 531 | connection. |
532 | Once the number of failures reaches half this value, | |
533 | additional failures are logged. | |
534 | The default is 6. | |
588df31a | 535 | .It Cm MaxStartups |
536 | Specifies the maximum number of concurrent unauthenticated connections to the | |
b74c3b8c | 537 | SSH daemon. |
588df31a | 538 | Additional connections will be dropped until authentication succeeds or the |
539 | .Cm LoginGraceTime | |
540 | expires for a connection. | |
541 | The default is 10. | |
542 | .Pp | |
543 | Alternatively, random early drop can be enabled by specifying | |
544 | the three colon separated values | |
545 | .Dq start:rate:full | |
f09ffbdb | 546 | (e.g. "10:30:60"). |
32cfd177 | 547 | .Xr sshd 8 |
588df31a | 548 | will refuse connection attempts with a probability of |
549 | .Dq rate/100 | |
550 | (30%) | |
551 | if there are currently | |
552 | .Dq start | |
553 | (10) | |
554 | unauthenticated connections. | |
555 | The probability increases linearly and all connection attempts | |
556 | are refused if the number of unauthenticated connections reaches | |
557 | .Dq full | |
558 | (60). | |
559 | .It Cm PasswordAuthentication | |
560 | Specifies whether password authentication is allowed. | |
561 | The default is | |
562 | .Dq yes . | |
563 | .It Cm PermitEmptyPasswords | |
564 | When password authentication is allowed, it specifies whether the | |
565 | server allows login to accounts with empty password strings. | |
566 | The default is | |
567 | .Dq no . | |
2fefbadf | 568 | .It Cm PermitOpen |
569 | Specifies the destinations to which TCP port forwarding is permitted. | |
570 | The forwarding specification must be one of the following forms: | |
571 | .Pp | |
572 | .Bl -item -offset indent -compact | |
573 | .It | |
574 | .Cm PermitOpen | |
575 | .Sm off | |
576 | .Ar host : port | |
577 | .Sm on | |
578 | .It | |
579 | .Cm PermitOpen | |
580 | .Sm off | |
581 | .Ar IPv4_addr : port | |
582 | .Sm on | |
583 | .It | |
584 | .Cm PermitOpen | |
585 | .Sm off | |
586 | .Ar \&[ IPv6_addr \&] : port | |
587 | .Sm on | |
588 | .El | |
589 | .Pp | |
ea46e550 | 590 | Multiple forwards may be specified by separating them with whitespace. |
2fefbadf | 591 | An argument of |
592 | .Dq any | |
593 | can be used to remove all restrictions and permit any forwarding requests. | |
f22506ff | 594 | By default all port forwarding requests are permitted. |
588df31a | 595 | .It Cm PermitRootLogin |
667e4135 | 596 | Specifies whether root can log in using |
588df31a | 597 | .Xr ssh 1 . |
598 | The argument must be | |
599 | .Dq yes , | |
600 | .Dq without-password , | |
b74c3b8c | 601 | .Dq forced-commands-only , |
588df31a | 602 | or |
603 | .Dq no . | |
604 | The default is | |
605 | .Dq yes . | |
606 | .Pp | |
607 | If this option is set to | |
b74c3b8c | 608 | .Dq without-password , |
8a4c4ee4 | 609 | password authentication is disabled for root. |
588df31a | 610 | .Pp |
611 | If this option is set to | |
b74c3b8c | 612 | .Dq forced-commands-only , |
588df31a | 613 | root login with public key authentication will be allowed, |
614 | but only if the | |
615 | .Ar command | |
616 | option has been specified | |
617 | (which may be useful for taking remote backups even if root login is | |
3cbc677d | 618 | normally not allowed). |
619 | All other authentication methods are disabled for root. | |
588df31a | 620 | .Pp |
621 | If this option is set to | |
b74c3b8c | 622 | .Dq no , |
667e4135 | 623 | root is not allowed to log in. |
d20f3c9e | 624 | .It Cm PermitTunnel |
625 | Specifies whether | |
626 | .Xr tun 4 | |
627 | device forwarding is allowed. | |
a4f24bf8 | 628 | The argument must be |
629 | .Dq yes , | |
06fa4ac1 | 630 | .Dq point-to-point |
631 | (layer 3), | |
632 | .Dq ethernet | |
633 | (layer 2), or | |
a4f24bf8 | 634 | .Dq no . |
06fa4ac1 | 635 | Specifying |
636 | .Dq yes | |
637 | permits both | |
638 | .Dq point-to-point | |
639 | and | |
640 | .Dq ethernet . | |
d20f3c9e | 641 | The default is |
642 | .Dq no . | |
f00bab84 | 643 | .It Cm PermitUserEnvironment |
644 | Specifies whether | |
645 | .Pa ~/.ssh/environment | |
35453849 | 646 | and |
f00bab84 | 647 | .Cm environment= |
648 | options in | |
649 | .Pa ~/.ssh/authorized_keys | |
35453849 | 650 | are processed by |
b74c3b8c | 651 | .Xr sshd 8 . |
f00bab84 | 652 | The default is |
653 | .Dq no . | |
35453849 | 654 | Enabling environment processing may enable users to bypass access |
655 | restrictions in some configurations using mechanisms such as | |
656 | .Ev LD_PRELOAD . | |
588df31a | 657 | .It Cm PidFile |
baa08b92 | 658 | Specifies the file that contains the process ID of the |
32cfd177 | 659 | SSH daemon. |
588df31a | 660 | The default is |
661 | .Pa /var/run/sshd.pid . | |
662 | .It Cm Port | |
663 | Specifies the port number that | |
b74c3b8c | 664 | .Xr sshd 8 |
588df31a | 665 | listens on. |
666 | The default is 22. | |
667 | Multiple options of this type are permitted. | |
668 | See also | |
669 | .Cm ListenAddress . | |
670 | .It Cm PrintLastLog | |
671 | Specifies whether | |
b74c3b8c | 672 | .Xr sshd 8 |
329a8666 | 673 | should print the date and time of the last user login when a user logs |
674 | in interactively. | |
588df31a | 675 | The default is |
676 | .Dq yes . | |
677 | .It Cm PrintMotd | |
678 | Specifies whether | |
b74c3b8c | 679 | .Xr sshd 8 |
588df31a | 680 | should print |
681 | .Pa /etc/motd | |
682 | when a user logs in interactively. | |
683 | (On some systems it is also printed by the shell, | |
684 | .Pa /etc/profile , | |
685 | or equivalent.) | |
686 | The default is | |
687 | .Dq yes . | |
688 | .It Cm Protocol | |
689 | Specifies the protocol versions | |
b74c3b8c | 690 | .Xr sshd 8 |
94ad46d1 | 691 | supports. |
588df31a | 692 | The possible values are |
b74c3b8c | 693 | .Sq 1 |
588df31a | 694 | and |
b74c3b8c | 695 | .Sq 2 . |
588df31a | 696 | Multiple versions must be comma-separated. |
697 | The default is | |
698 | .Dq 2,1 . | |
94ad46d1 | 699 | Note that the order of the protocol list does not indicate preference, |
700 | because the client selects among multiple protocol versions offered | |
701 | by the server. | |
702 | Specifying | |
703 | .Dq 2,1 | |
704 | is identical to | |
705 | .Dq 1,2 . | |
588df31a | 706 | .It Cm PubkeyAuthentication |
707 | Specifies whether public key authentication is allowed. | |
708 | The default is | |
709 | .Dq yes . | |
710 | Note that this option applies to protocol version 2 only. | |
588df31a | 711 | .It Cm RhostsRSAAuthentication |
712 | Specifies whether rhosts or /etc/hosts.equiv authentication together | |
713 | with successful RSA host authentication is allowed. | |
714 | The default is | |
715 | .Dq no . | |
716 | This option applies to protocol version 1 only. | |
717 | .It Cm RSAAuthentication | |
718 | Specifies whether pure RSA authentication is allowed. | |
719 | The default is | |
720 | .Dq yes . | |
721 | This option applies to protocol version 1 only. | |
722 | .It Cm ServerKeyBits | |
723 | Defines the number of bits in the ephemeral protocol version 1 server key. | |
724 | The minimum value is 512, and the default is 768. | |
725 | .It Cm StrictModes | |
726 | Specifies whether | |
b74c3b8c | 727 | .Xr sshd 8 |
588df31a | 728 | should check file modes and ownership of the |
729 | user's files and home directory before accepting login. | |
730 | This is normally desirable because novices sometimes accidentally leave their | |
731 | directory or files world-writable. | |
732 | The default is | |
733 | .Dq yes . | |
734 | .It Cm Subsystem | |
f09ffbdb | 735 | Configures an external subsystem (e.g. file transfer daemon). |
d66ce1a1 | 736 | Arguments should be a subsystem name and a command (with optional arguments) |
737 | to execute upon subsystem request. | |
588df31a | 738 | The command |
739 | .Xr sftp-server 8 | |
740 | implements the | |
741 | .Dq sftp | |
742 | file transfer subsystem. | |
743 | By default no subsystems are defined. | |
744 | Note that this option applies to protocol version 2 only. | |
745 | .It Cm SyslogFacility | |
746 | Gives the facility code that is used when logging messages from | |
32cfd177 | 747 | .Xr sshd 8 . |
588df31a | 748 | The possible values are: DAEMON, USER, AUTH, LOCAL0, LOCAL1, LOCAL2, |
749 | LOCAL3, LOCAL4, LOCAL5, LOCAL6, LOCAL7. | |
750 | The default is AUTH. | |
fd573618 | 751 | .It Cm TCPKeepAlive |
752 | Specifies whether the system should send TCP keepalive messages to the | |
753 | other side. | |
754 | If they are sent, death of the connection or crash of one | |
755 | of the machines will be properly noticed. | |
756 | However, this means that | |
757 | connections will die if the route is down temporarily, and some people | |
758 | find it annoying. | |
759 | On the other hand, if TCP keepalives are not sent, | |
760 | sessions may hang indefinitely on the server, leaving | |
761 | .Dq ghost | |
762 | users and consuming server resources. | |
763 | .Pp | |
764 | The default is | |
765 | .Dq yes | |
766 | (to send TCP keepalive messages), and the server will notice | |
767 | if the network goes down or the client host crashes. | |
768 | This avoids infinitely hanging sessions. | |
769 | .Pp | |
770 | To disable TCP keepalive messages, the value should be set to | |
771 | .Dq no . | |
c5a7d788 | 772 | .It Cm UseDNS |
773 | Specifies whether | |
b74c3b8c | 774 | .Xr sshd 8 |
102c77c2 | 775 | should look up the remote host name and check that |
c5a7d788 | 776 | the resolved host name for the remote IP address maps back to the |
777 | very same IP address. | |
778 | The default is | |
779 | .Dq yes . | |
588df31a | 780 | .It Cm UseLogin |
781 | Specifies whether | |
782 | .Xr login 1 | |
783 | is used for interactive login sessions. | |
784 | The default is | |
785 | .Dq no . | |
786 | Note that | |
787 | .Xr login 1 | |
788 | is never used for remote command execution. | |
789 | Note also, that if this is enabled, | |
790 | .Cm X11Forwarding | |
791 | will be disabled because | |
792 | .Xr login 1 | |
793 | does not know how to handle | |
794 | .Xr xauth 1 | |
a4e5acef | 795 | cookies. |
796 | If | |
588df31a | 797 | .Cm UsePrivilegeSeparation |
798 | is specified, it will be disabled after authentication. | |
72c35df7 | 799 | .It Cm UsePAM |
d5c67850 | 800 | Enables the Pluggable Authentication Module interface. |
801 | If set to | |
802 | .Dq yes | |
803 | this will enable PAM authentication using | |
804 | .Cm ChallengeResponseAuthentication | |
05059810 | 805 | and |
806 | .Cm PasswordAuthentication | |
807 | in addition to PAM account and session module processing for all | |
808 | authentication types. | |
d5c67850 | 809 | .Pp |
810 | Because PAM challenge-response authentication usually serves an equivalent | |
811 | role to password authentication, you should disable either | |
812 | .Cm PasswordAuthentication | |
813 | or | |
814 | .Cm ChallengeResponseAuthentication. | |
815 | .Pp | |
816 | If | |
817 | .Cm UsePAM | |
818 | is enabled, you will not be able to run | |
819 | .Xr sshd 8 | |
820 | as a non-root user. | |
821 | The default is | |
a83a3125 | 822 | .Dq no . |
588df31a | 823 | .It Cm UsePrivilegeSeparation |
824 | Specifies whether | |
b74c3b8c | 825 | .Xr sshd 8 |
588df31a | 826 | separates privileges by creating an unprivileged child process |
a4e5acef | 827 | to deal with incoming network traffic. |
828 | After successful authentication, another process will be created that has | |
829 | the privilege of the authenticated user. | |
830 | The goal of privilege separation is to prevent privilege | |
588df31a | 831 | escalation by containing any corruption within the unprivileged processes. |
832 | The default is | |
833 | .Dq yes . | |
588df31a | 834 | .It Cm X11DisplayOffset |
835 | Specifies the first display number available for | |
b74c3b8c | 836 | .Xr sshd 8 Ns 's |
588df31a | 837 | X11 forwarding. |
b74c3b8c | 838 | This prevents sshd from interfering with real X11 servers. |
588df31a | 839 | The default is 10. |
840 | .It Cm X11Forwarding | |
841 | Specifies whether X11 forwarding is permitted. | |
e6fe1bab | 842 | The argument must be |
843 | .Dq yes | |
844 | or | |
845 | .Dq no . | |
588df31a | 846 | The default is |
847 | .Dq no . | |
e6fe1bab | 848 | .Pp |
849 | When X11 forwarding is enabled, there may be additional exposure to | |
850 | the server and to client displays if the | |
b74c3b8c | 851 | .Xr sshd 8 |
e6fe1bab | 852 | proxy display is configured to listen on the wildcard address (see |
853 | .Cm X11UseLocalhost | |
b74c3b8c | 854 | below), though this is not the default. |
e6fe1bab | 855 | Additionally, the authentication spoofing and authentication data |
856 | verification and substitution occur on the client side. | |
857 | The security risk of using X11 forwarding is that the client's X11 | |
b74c3b8c | 858 | display server may be exposed to attack when the SSH client requests |
e6fe1bab | 859 | forwarding (see the warnings for |
860 | .Cm ForwardX11 | |
861 | in | |
be193d89 | 862 | .Xr ssh_config 5 ) . |
e6fe1bab | 863 | A system administrator may have a stance in which they want to |
864 | protect clients that may expose themselves to attack by unwittingly | |
865 | requesting X11 forwarding, which can warrant a | |
866 | .Dq no | |
867 | setting. | |
868 | .Pp | |
869 | Note that disabling X11 forwarding does not prevent users from | |
870 | forwarding X11 traffic, as users can always install their own forwarders. | |
588df31a | 871 | X11 forwarding is automatically disabled if |
872 | .Cm UseLogin | |
873 | is enabled. | |
874 | .It Cm X11UseLocalhost | |
875 | Specifies whether | |
b74c3b8c | 876 | .Xr sshd 8 |
588df31a | 877 | should bind the X11 forwarding server to the loopback address or to |
a4e5acef | 878 | the wildcard address. |
879 | By default, | |
b74c3b8c | 880 | sshd binds the forwarding server to the loopback address and sets the |
588df31a | 881 | hostname part of the |
882 | .Ev DISPLAY | |
883 | environment variable to | |
884 | .Dq localhost . | |
b3641662 | 885 | This prevents remote hosts from connecting to the proxy display. |
588df31a | 886 | However, some older X11 clients may not function with this |
887 | configuration. | |
888 | .Cm X11UseLocalhost | |
889 | may be set to | |
890 | .Dq no | |
891 | to specify that the forwarding server should be bound to the wildcard | |
892 | address. | |
893 | The argument must be | |
894 | .Dq yes | |
895 | or | |
896 | .Dq no . | |
897 | The default is | |
898 | .Dq yes . | |
899 | .It Cm XAuthLocation | |
57ff5eeb | 900 | Specifies the full pathname of the |
588df31a | 901 | .Xr xauth 1 |
902 | program. | |
903 | The default is | |
904 | .Pa /usr/X11R6/bin/xauth . | |
905 | .El | |
ef1c6497 | 906 | .Sh TIME FORMATS |
32cfd177 | 907 | .Xr sshd 8 |
588df31a | 908 | command-line arguments and configuration file options that specify time |
909 | may be expressed using a sequence of the form: | |
910 | .Sm off | |
36535ee6 | 911 | .Ar time Op Ar qualifier , |
588df31a | 912 | .Sm on |
913 | where | |
914 | .Ar time | |
915 | is a positive integer value and | |
916 | .Ar qualifier | |
917 | is one of the following: | |
918 | .Pp | |
919 | .Bl -tag -width Ds -compact -offset indent | |
874d319b | 920 | .It Aq Cm none |
588df31a | 921 | seconds |
922 | .It Cm s | Cm S | |
923 | seconds | |
924 | .It Cm m | Cm M | |
925 | minutes | |
926 | .It Cm h | Cm H | |
927 | hours | |
928 | .It Cm d | Cm D | |
929 | days | |
930 | .It Cm w | Cm W | |
931 | weeks | |
932 | .El | |
933 | .Pp | |
934 | Each member of the sequence is added together to calculate | |
935 | the total time value. | |
936 | .Pp | |
937 | Time format examples: | |
938 | .Pp | |
939 | .Bl -tag -width Ds -compact -offset indent | |
940 | .It 600 | |
941 | 600 seconds (10 minutes) | |
942 | .It 10m | |
943 | 10 minutes | |
944 | .It 1h30m | |
945 | 1 hour 30 minutes (90 minutes) | |
946 | .El | |
947 | .Sh FILES | |
948 | .Bl -tag -width Ds | |
949 | .It Pa /etc/ssh/sshd_config | |
950 | Contains configuration data for | |
32cfd177 | 951 | .Xr sshd 8 . |
588df31a | 952 | This file should be writable by root only, but it is recommended |
953 | (though not necessary) that it be world-readable. | |
954 | .El | |
be193d89 | 955 | .Sh SEE ALSO |
956 | .Xr sshd 8 | |
588df31a | 957 | .Sh AUTHORS |
958 | OpenSSH is a derivative of the original and free | |
959 | ssh 1.2.12 release by Tatu Ylonen. | |
960 | Aaron Campbell, Bob Beck, Markus Friedl, Niels Provos, | |
961 | Theo de Raadt and Dug Song | |
962 | removed many bugs, re-added newer features and | |
963 | created OpenSSH. | |
964 | Markus Friedl contributed the support for SSH | |
965 | protocol versions 1.5 and 2.0. | |
966 | Niels Provos and Markus Friedl contributed support | |
967 | for privilege separation. |